For drilling holes, e.g., horizontal, vertical, and/or slanted holes, into a medium, e.g., concrete, stone, etc., a drilling frame motor support and drill require support, especially during the earlier stages of drilling, where the drill has not penetrated a substantial distance into the medium. During drilling of deeper holes, typical drills provide for relatively rapid progress at the beginning of the drilling operation and very slow progress toward the end. Drills of substantial length, e.g., one foot long drills, may become constricted by the walls of the hole as the drill progresses into the medium. Reduction in progress may be attributed to reduced oscillation of the motor end of the drill and/or reduced vibration of the drill support, which is increasingly constrained as the drill progresses further into the material and the hole gets deeper.
A known technique to address the limitations of this procedure is to drill a larger hole first and then use progressively smaller drills. For example, when drilling a horizontal hole into a concrete wall with a 4½ inch core drill bit spinning at 200 to 300 rpm with a pushing force of 100 to 150 pounds, the bit or the material cutting face may glaze over and experience a reduction in cutting speed (i.e., drilling depth per unit time) to less than ⅓ the cutting speed experienced during the initial stages of drilling. The speed may be increased by orbiting or oscillating the rotational axis of the bit, e.g., using a 2 to 5, e.g., 3 to 4 degree orbit. The orbiting or oscillation may involve moving the rear portion of the bit, e.g., in a circular motion, with respect to the axis of the hole being drilled, with the tip of the drill remaining substantially in a constant radial location, typically centered at the axis of the hole. In order to accommodate the motion of the drill bit, graduated bit sizes may be used during the progression of the drilling, such that larger diameter bits are used at the early stages and progressively smaller diameter bits are used as the drill axially progresses to form the hole. In this manner, adequate clearance may be provided to orbit or oscillate the bit. The technique of drilling a large hole first and then using progressively smaller drill bits as the hole gets deeper permits vibrational and/or rotational oscillation of the drill motor end and therefore allows for faster drilling progress as the drill works toward the end of the hole.
Although the conventional orbiting/oscillating technique may improve drilling performance, the use of multiple drills is tedious and the resulting hole may not be structurally and/or visually acceptable. For example, in renovation situations where large pipes such as electrical feeders or sprinkler mains must be passed through existing masonry partitions in full view, this technique may be visually unappealing and result in the removal of more material than necessary. Additionally, using multiple drills of different sizes increases time, labor, and cost.
Using a core drill with abrasive teeth diamond coated teeth) is common for holes variously above an inch and half in diameter in masonry materials like concrete and stone. Experience has shown that oscillating the drill motor while the teeth are (partially) contacting the face of the material makes the drilling process faster. For drilling deeper holes, common advice is to have a larger hole at the start of the process and as the hole progresses deeper, to use progressively smaller drills. This permits space at the beginning of the hole for orbital motion of the drill motor. As indicated above, moving the drill motor end of the drill in an orbital path makes the drilling process faster. The design of the improved bit described here produces faster drilling while allowing constant diameter holes without moving the drill motor.
There is a need for a drill bit that provides increased axial drilling speed without the need to orbit or oscillate the proximal portion of the drill bit. Moreover, there is a need for a drill bit that allows a relatively constant hole diameter along the length of the drilled hole and avoids unnecessary removal of material, such as caused by successively drilling holes of differing diameters according to the method described above. Still further, there is a need for a drill bit and drilling method that allows for more uniform and visually appealing results.